One of the drawbacks of the Ordinary Portland cement industry is its vast carbon dioxide emission quantities causing environmental and health problems. These problems can be faced by reducing the production of OPC by introducing alternative and supplementary cementitious materials. The present study aims to use mafic rock powder from the ophiolitic meta-gabbroic rock sequences as an alternative substitute for cement and its effect on the fresh and hardened properties of cement composite pastes. The main objective of this study is to track the pozzolanic activity of these alternative materials through physico-mechanical properties, mineralogy, microstructure, and heat of hydration. The studied mafic rock was thoroughly analyzed using a polarized light microscope, XRD, XRF, SEM, DTA/TG, and FTIR, in addition to physical properties. Seven mixes of cement paste composites using up to 30% mafic rock powder were prepared. Several hydration and attack regimes were involved, starting with tap water hydration for up to 28 days, followed by adverse attack conditions such as seawater and sulfate attack media for up to 3 months. The kinetics of hydration, mineralogical, and morphological investigations of the prepared composites were followed over different hydration and attack periods. An improvement in the physico-mechanical properties with notable progress up to 10% replacement was observed. The durability results of all mixes exhibited an outstanding enhancement regarding resistance to strength loss compared with the reference mix. The novelty of the current research is the recording of a significant effect of a minute addition of studied mafic rock powder on the hydration kinetics and the hydration products. Utilizing mafic rock powder up to 10% was recommended in producing different low costs cement-based materials. The partial replacement of cement by mafic rock powder up to 10% decreased the energy needed to produce a ton of binder by 13.75%. •No pozzolanic activity for mafic rock, even though it passed the strength activity index (SAI).•A slight decrease in mix water, while a remarkable prolongation in setting times with addition.•An improvement in physico-mechanical properties with a notable advance up to 10% addition.•An outstanding resistance against seawater and sulfate attack was noticed with replacement.•A reduction in energy consumed for blended cement production by 13.75% at 10% addition.